1. Field of the Invention
This invention relates to a cleaning method for use in microelectronics manufacturing, and more particularly to a non-corrosive method for removing photoresist and plasma etch residues formed on wafer substrates after plasma etching of metal layers or oxide layers deposited on the substrates.
2. Brief Description of Art
In the manufacture of microcircuits, positive photoresists are used as an intermediate mask for transferring an original mask pattern of a reticule onto wafer substrates by means of a series of photolithography and plasma etching steps. One of the final steps in the microcircuit manufacturing process is the removal of the patterned photoresist films from the substrates. In general, this step is affected by one of two methods. One method involves a wet stripping step in which the photoresist-covered substrate is brought into contact with a photoresist stripper solution that consists primarily of an organic solvent and an amine. However, stripper solutions cannot completely and reliably remove the photoresist films, especially if the photoresist films have been exposed to UV radiation and plasma treatments during fabrication. Some photoresist films become highly crosslinked by such treatments and are more difficult to dissolve in the stripper solution. In addition, the chemicals used in these conventional wet stripping methods are sometimes ineffective for removing inorganic residual materials formed during the plasma etching of metal or oxide layers with halogen-containing gases.
An alternative method of removing a photoresist film involves exposing a photoresist-coated wafer to oxygen plasma in order to burn the resist film from the substrate surface in a process known as oxygen plasma ashing. Oxygen plasma ashing has become more popular in the microcircuit manufacturing process because it is carried out in a vacuum chamber and, hence, is expected to be less susceptible to airborne particulate or metallic contamination. However, oxygen plasma ashing is also not fully effective in removing plasma etching residues noted above. Instead, removal of these plasma etching residues must be accomplished by subsequently exposing the photoresist film to certain alkaline solutions. Several commercial products are now available to clean the plasma etching residues left by plasma etching followed by oxygen ashing. For example, EKC 265, available from EKC Technology, Inc., is a plasma etching cleaning solution composed of water, alkanolamine, catechol and hydroxylamine Such a composition is disclosed in U.S. Pat. No. 5,279,771 to Lee. ACT 935, available from Ashland Chemical, is another plasma etching cleaning solution and is composed of water, alkanolamine and hydroxylamine. In both cases, hydroxylamine is used as a corrosion inhibitor. R-10, a post-strip rinse available from Mitsubishi Gas Chemical, is composed of water, alkanolamine and a sugar alcohol, wherein the sugar alcohol acts as a corrosion inhibitor.
Although these commercial products can effectively dissolve plasma etching residues, the combination of water and alkanolamine contained therein can also attack the metallic layers deposited patternwise on the substrate. The addition of a corrosion inhibitor to these products can mitigate to a certain extent, the unwanted attack on the metallic layers and oxide layers deposited on the substrate. However, since these products have a pH above 11, even in the presence of a corrosion inhibitor, they may attack certain corrosion-sensitive metal layers. Particularly, metal layers such as aluminum or aluminum alloys (e.g., Al--Cu--Si), titanium nitride, titanium tungsten and the like are particularly corrosion sensitive. Furthermore, while the addition of a suitable corrosion inhibitor is essential to prevent corrosion of the substrate metal layers, the corrosion inhibitor must not inhibit the removal of the plasma etching residue.
It is difficult to balance effective plasma etching residue removal corrosion inhibition because chemical compositions of the plasma etching residues are generally similar to those of the metal layers or oxide layers on the substrate. The alkanolamine used in the prior art cleaning compositions was oftentimes found to attack both the plasma etching residue and the substrate metal layers. Moreover, if a post-cleaner rinse such as isopropyl alcohol is not used, the corrosion could be very severe. In addition, some types of the corrosion inhibitors have been found to retard plasma etching residue removal. There has also always been a tradeoff between speed of plasma etching residue removal and substrate metal layer corrosion inhibition. Accordingly, there has remained a need for a method of quickly and effectively removing the plasma etching residues without causing metal layer corrosion
Several other patents in the photoresist stripper/cleaner application field exist as follows, although none of them disclose the use of the method or compositions of the present invention:
Japanese Patent Application No. 7-028254, assigned to Kanto Kagaku, discloses a non-corrosive resist removal liquid comprising a sugar alcohol, an alcohol amine, water, and a quaternary ammonium hydroxide.
PCT Published Patent Application No. WO 88-05813 teaches a positive or negative photoresist stripper containing butyrolactone or caprolactone, quaternary ammonium hydroxide compound, and optionally, a nonionic surfactant.
U.S. Pat. No. 4,239,661 to Muraoka et al. discloses a surface-treating agent comprising an aqueous solution of 0.01% to 20% trialkyl (hydroxyalkyl) ammonium hydroxide. This agent is useful in removing organic and inorganic contaminants deposited on the surface of intermediate semiconductor products.
U.S. Pat. No. 4,904,571 to Miyashita et al. teaches printed circuit board photoresist stripper composition containing a solvent (e.g., water, alcohols, ethers, ketones, and the like), an alkaline compound dissolved in the solvent, including quaternary ammonium hydroxide, and a borohydride compound dissolved in the solvent.
U.S. Pat. No. 5,091,103 to Dean et al. teaches a positive photoresist stripping composition containing: (A) N-alkyl-2-pyrrolidone; (B) 1,2-propanediol; and (C) tetraalkylammonium hydroxide.
U.S. Pat. No. 5,139,607 to Ward et al. teaches positive and negative photoresist stripping composition containing: (A) tetrahydrofurfuryl alcohol; (B) a polyhydric alcohol (e.g., ethylene glycol or propylene glycol); (C) the reaction product of furfuryl alcohol and an alkylene oxide; (D) a water-soluble Bronstead base type hydroxide compound (e.g., alkali metal hydroxide, ammonium hydroxide and tetramethyl ammonium hydroxide); and (E) water. Optionally, the composition may also contain up to 1% of a nonionic surfactant.
U.S. Pat. No. 5,174,816 to Aoyama et al. discloses a composition for removing chlorine remaining on the surface of an aluminum line pattern substrate after dry etching, which composition comprises an aqueous solution containing 0.01 to 15% by weight of a quaternary ammonium hydroxide, such as trimethyl (2-hydroxyethyl) ammonium hydroxide, and 0.1 to 20% by weight of sugar or sugar alcohol, such as xylitol, mannose, glucose and the like.
Other compositions used to strip photoresist include a solution of H.sub.2 SO.sub.4 and an oxidizing agent such as H.sub.2 O.sub.2 that oxidizes, and thus decomposes organic photoresists. However, solutions containing strong acids and oxidizing agents are hazardous to handle, must be applied at elevated temperatures, and require a hot deionized (DI) water rinse to prevent sulfates from crystallizing on the substrate. Also, such solutions have a short active life as the oxidizing agent readily decomposes. Thus, it is necessary to frequently replenish the solutions. The need for solution replenishment renders the process both hazardous and economically inefficient.
Compared to the foregoing process, the use of a mixture of H.sub.2 SO.sub.4 and ozone (O.sub.3) provides for improved active life since O.sub.3 can be bubbled continuously into the solution to maintain oxidation efficiency. However, when plasma etch or a high concentration of arsenic is used in ion implantation, the photoresist film is not completely removed. Also, O.sub.3 has limited solubility in H.sub.2 SO.sub.4. U.S. Pat. No. 5,378,317 discloses the application of a solution of H.sub.2 SO4/H.sub.2 O.sub.2 or oxygen plasma ashing followed by a treatment with ozone containing water. However, this process is not capable of removing plasma etch residues such as aluminum oxide, silicon oxide, or aluminum chloride.
Therefore, there remains a need for a method for removing photoresist and plasma etch residues from substrates. Additionally, there remains a need for such a method that does not deleteriously affect the substrate. Further, there remains a need for such a method that uses aqueous-based, non-hazardous cleaning compositions that will not harm the environment.